The use of POAs and HPAs for the catalytic air oxidation of alkanes such as butane is known. [See, for example, M. Ai, Partial Oxidation of n-Butane with Heteropoly Compound-based Catalysts, Proceedings of the 8th International Congress on Catalysis, Berlin, 1984, Verlag Chemie Vol. 5, page 475]. However, these oxidations have been high temperature, vapor phase reactions which are, by their nature, prone to by-products, including carbon oxides (CO and CO.sub.2) and water, or have been oxidations of alkenes and alcohols which are quite easy to oxidize. In addition, selective, low temperature, liquid phase oxidation of alkanes to alcohols are notoriously more difficult to effect than vapor phase oxidation, whatever the catalyst.
HPAs and POAs, both in general and those used in our invention, and their preparation are thoroughly described in Heteropoly and Isopoly Oxo-metalates, Pope et al, Springer-Verlag, New York 1983. In order to clarify the terminology used in the art, consider first a specific precursor used in our invention, H.sub.3 PW.sub.12 O.sub.40. Since the cations in this material are hydrogen, the compound is a heteropolyacid. If the cations are not hydrogen but are metals such as an alkali metal, potassium, sodium, or lithium, or are ammonium, as in K.sub.3 PW.sub.12 O.sub.40 or (NH.sub.4).sub.3 PW.sub.12 O.sub.40, then it is obviously no longer an acid, and is referred to as a polyoxoanion.
As described in Pope, HPAs and POAs are cage-like structures with a primary, generally centrally located atom(s) surrounded by the cage framework which contains a plurality of other metal atoms, the same or different, bonded to oxygen atoms. Since the central metal atom is different from the other atoms, it is described as "hetero." The other metal atoms are transition metals and have oxygen bonding such as ##STR1##